Add unit tests for utilities

[fluix-dev]

This issue tracks the completion of unit tests for judge utilities available in /judge/utils.

• [ ] #1415 will complete the following

  • [x] cachedict
  • [x] camo
  • [x] diggpaginator
  • [x] file_cache
  • [x] infinite_paginator
  • [x] opengraph
  • [x] ranker
  • [x] stats
  • [x] strings
  • [x] two_factor
  • [x] unicode

• [ ] Remaining

  • [ ] caniuse
  • [ ] celery
  • [ ] mathoid
  • [ ] problems
  • [ ] problem_data
  • [ ] raw_sql
  • [ ] recaptcha
  • [ ] subscription
  • [ ] texoid
  • [ ] tickets
  • [ ] timedelta
  • [ ] pwned - our version has been stripped down, but original tests are available here.
  • [ ] views

[quantum5]

I don't necessarily agree with the third party exception. We still need tests for it, especially since it was manually stripped down.

[fluix-dev]

We still need tests for it, especially since it was manually stripped down.

Didn't know about this, fair enough then, I'll add it to the list with a note.